The present invention relates human-machine interfaces and, more particularly, to a touch screen system and to a corresponding methodology for operating a touch screen system.
Various types of touch screen monitors have been developed to facilitate user interaction with graphical user interfaces (GUIs). Touch screens are gaining popularity for numerous applications, including point-of-information kiosks, vending, electronic catalogs, in-store locators, corporate training, gaming, lottery, and amusement, multimedia marketing, banking/financial transactions, ticket sales, interactive education, multimedia demos, museum displays, and the like. A touch screen generally employs one of four types of touch technologies: capacitive, resistive, infrared, and surface acoustic wave (SAW). In general, capacitive and resistive touch technologies both rely on overlays, whereas infrared and SAW configurations typically do not require overlays.
By way of illustration, an analog resistive screen is formed of a sandwich of Mylar and plastic or glass separated by substantially transparent elastic spacers. The inside surfaces of the sandwich are coated with a uniform transparent thin film, such as a conductive coating. In operation, a voltage is alternately applied along horizontal and vertical axes of the screen. When a user depresses the Mylar overlay so that its conductive layer contacts the energized layer, the resulting voltage is sensed and transmitted to a controller that converts the signal to an indication of touch location.
In a capacitive type of touch screen, a glass panel is coated with a conductive coating that is fused into the glass. The coating is connected to electrodes located at edges of the screen. Each electrode is connected to an oscillator circuit. When a user touches the screen, the body capacitance of the user causes a change in the impedance of the screen. The impedance change causes the oscillator frequencies to vary, and the frequency differentials are converted into a corresponding X-Y coordinate.
The IR technology employs an array of infrared (IR) light emitting diode (LED)/photodetector pairs mounted in a frame. In operation, the LED/photodetector array is continuously and sequentially scanned horizontally and then vertically. When a user touches the display breaking one or more of the light beams, the X-Y position of the touch can be transmitted to a controller or host computer. In order to increase the maximum resolution of an IR touch screen to approximately double the number of LED/photodetector pairs, an interpolation technique can be employed. Using interpolation, when an odd number of beams is broken along either axis, the X or Y coordinate of the center beam is transmitted, but when an even number of beams is broken, the coordinates of the interpolated beam are calculated and transmitted to the host computer.
Today, most commercial acoustic touch screen systems employ surface acoustic waves (SAWs) as the acoustic mode propagating in a faceplate, although other modes can be used, such as horizontally or transversely polarized shear waves. In one particular type of SAW touch screen system (sometimes referred to as the Adler system), the presence and location of a finger or stylus on a faceplate is determined based on disruption of one or more SAWs propagating on the screen. This method propagates a SAW on one side of the faceplate in a beam that is near an edge of the screen. A series of reflectors, which can be gratings, are located along the edge of the screen, each of which reflects a portion of the energy across the faceplate at about 90xc2x0 relative to the edge and the direction in which the beam is traveling. The density of reflectors is varied so that the amplitude of the signals propagating across the faceplate is nearly constant. A second set of reflectors are located at the opposite edge of the screen, which reflect the SAW into a beam propagating substantially parallel to the edge. The spacing of the reflectors is chosen so that the multiple beams propagating across the faceplate cover substantially the entire surface. The arrival time of the various beams at the receiving transducer increases monotonically as the total path length increases.
By way of illustration, when a finger or other object contacts the screen, it interrupts the SAW causing a decrease in the received amplitude corresponding to the position of the finger or object. As a result, this approach bases detection on the blockage or disruption of a transmitted SAW and on the spacing of the multiplicity of beams for spatial resolution.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides system and method for implementing a touch screen system. The system includes a substrate having a surface and at least three acoustic wave transducers at spaced apart locations. One or more transducers are operative to transmit an acoustic wave that propagates along the substrate surface. The other transducers are operative to receive acoustic waves that propagate along the substrate surface. A control system associated with at least the receiving transducers are operative to determine which part of the substrate surface is perturbed, such as by a finger, a stylus, or other object. The location of the perturbation can be determined based on when the acoustic wave is transmitted and when a corresponding acoustic wave is received at each of the second and third transducers, which corresponding wave was reflected or scattered from the part of the substrate surface that was perturbed.
In accordance with a particular aspect of the present invention, time delays between transmission of the acoustic wave and receipt of the corresponding acoustic wave at the other transducers define respective ellipses. An intersection between such ellipses corresponds to a location of the part of the substrate surface that was perturbed. Thus, by detecting the time delays between transmission and receipt of acoustic waves relative to the transducers, coordinates on the substrate surface can be determined for each perturbation.
Another aspect of the present invention provides a method, which can be implemented as hardware and/or software, to discern a location at which a surface of a substrate is perturbed. The method includes transmitting an acoustic wave that propagates across a substrate surface. An acoustic wave is detected at two or more transducers. A first time value is set to a time delay between when the acoustic wave is transmitted and the detection at one of the transducers and a second time value is set to a time delay between when the acoustic wave is transmitted and the detection at another of the transducers. An indication of the location at which a surface of a substrate is perturbed, thus, can be determined based on the first and second time values.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.